Ground fault circuit interrupters (GFCIs) were developed to meet a pressing need for a device that was capable of detecting abnormal current flow (typically current flow from phase to ground) and in response thereto, interrupting power to the electrical system to which the device is connected. In such a manner, the device would help protect people from electric shock, fire and explosion. To provide a high degree of protection, the detection of ground fault current in the order of milliamps is required, while the load current flowing may range from 10 to 100 A.
While numerous prior art techniques are available for protecting against ground faults, two issues remain in the application of GFCIs in residential and commercial environments. Firstly the correct installation of the GFCI and secondly the reliability of the GFCI once installed.
When a ground fault is detected, a GFCI will interrupt both phase and neutral electrical lines. Thus, users are protected from phase to ground faults even if the phase and neutral wires have been inadvertently switched. Miswiring a GFCI device, however, can still be problematic. Receptacle, i.e., wall outlet, GFCIs can be wired to protect a single outlet, or they can be wired as a `through` device protecting not only the GFCI outlet itself but also outlets downstream from the device.
In addition, GFCIs are typically installed into the electrical system prior to electricity being applied, especially in new construction. Wiring a receptacle using the `through` arrangement carries with it the possibility of miswiring, since the wiring box contains two pairs of phase and neutral wires which are not always easily identifiable as line and load. Consequently, there is a real possibility that an installer might inadvertently connect the line side of the AC wiring to the load side of the GFCI and the load side of the AC wiring to the line side of the GFCI. While in this line/load reverse wiring condition, downstream electrical devices are still protected but any receptacles in the GFCI device itself are not protected, thus creating a potential hazard.
Currently, GFCIs are shipped with warning labels and detailed installation instructions, but these are not always read by installers and/or end users. Thus, there is a need for a means to determine when a line/load reverse wiring condition exists.
In addressing problems of reliability, it is noted that typically, a GFCI is connected to the premise electrical wiring system at the time of installation and is forgotten thereafter. The homeowner or contractor simply assumes that the GFCI they just installed will operate correctly years after it is installed. Unfortunately, this is not necessarily the case. Despite the efforts of manufacturers, GFCIs are still subject to a number of failure modes. These failure modes are typically caused by abnormal operating conditions such as poor AC supply quality, misuse or chemical action upon the internal parts of the GFCI.
To ensure reliability, many GFCI devices incorporate a TEST button that is located on the exterior of the device that when pressed, simulates a ground fault. This simulated ground fault causes the internal circuitry to respond as if a real ground fault had occurred. The majority of the internal components, circuitry and mechanical mechanisms are exercised and tested. If the internal mechanisms of the GFCI are working correctly, the contacts internal to the GFCI open thus removing power from the electrical circuit connected to the GFCI.
Following a test, the GFCI must be reset in order to return to its normal operating condition. This is typically achieved by pressing a RESET button also located on the exterior of the GFCI. Pressing the RESET button causes the circuit interrupter contacts to close either mechanically or electromechanically. Via instructions included with the device and/or via device labels, users are instructed to test the GFCI periodically (typically every 30 days) and replace devices that fail. In reality, however, most people ignore the instructions to test the device on a regular basis, testing the device infrequently, if at all, even when visible instructions and warnings are placed on the GFCI itself.
Another factor lowering reliability of GFCIs, in addition to the failure of users to test the GFCI, include power outages and the corresponding surges in power when power is restored. Power restoration can cause huge spikes of voltage and current to appear on the power line, thus creating the possibility of component failure. Therefore, it would be desirable if the GFCI was able to detect power being restored after a sufficiently long power outage and, in response, to force the user to test the device. Required testing of the GFCI after it has tripped due to a ground fault would also be beneficial, due to the possibility of abnormal currents and voltages that may occur during this time.
Thus, there is a need for a GFCI that is capable of communicating to a user the occasions that the device must be tested. Upon testing, the device should indicate whether it has been miswired and/or whether any portion of its internal components is not operating correctly.